An alternative Avrami equation to evaluate kinetic parameters of the interaction of Hg(II) with thin chitosan membranes

2003 ◽  
Vol 263 (2) ◽  
pp. 542-547 ◽  
Author(s):  
Elaine C.N. Lopes ◽  
Fernanda S.C. dos Anjos ◽  
Eunice F.S. Vieira ◽  
Antonio R. Cestari
e-Polymers ◽  
2008 ◽  
Vol 8 (1) ◽  
Author(s):  
Hossein Ali Khonakdar ◽  
Masoud Shiri ◽  
Ahmad Asadinezhad ◽  
Seyed Hassan Jafari ◽  
Mahdi Golriz

AbstractThe Avrami equation has been extensively used to describe the polymer crystallization kinetics. Evaluation of kinetic parameters of this equation is quite troublesome, calling for properly predetermining induction time. To avoid this problem, an analytical approach in terms of differential scanning calorimetry exotherm maximum point was adopted here so as to conveniently estimate the Avrami equation kinetic parameters both in isothermal and dynamic crystallization mode. In the case of dynamic crystallization under isokinetic conditions, a modified version of the Avrami model by Nakamura was employed and adequate predictions based on the derived formulas were obtained. However, due to the simplified assumptions of the Avrami theory, our adopted relations are only applicable to earlier stages of crystallization process and do not account for secondary crystallization.


2000 ◽  
Vol 15 (4) ◽  
pp. 1000-1007 ◽  
Author(s):  
Haoyue Zhang ◽  
Brian S. Mitchell

A new equation was developed for evaluating kinetic parameters in the isokinetic range of a phase transformation using nonisothermal calorimetric techniques. The Johnson–Mehl–Avrami equation was extended by considering that the transformation rate in an isothermal process can be translated into the nonisothermal transformation in an isokinetic range. The Avrami exponent, n, activation energy, E, and frequency factor, K0, were calculated from only one nonisothermal experiment by using the new kinetic equation for amorphous Se (a-Se), polysilane/polycarbosilane (PS/PCS), and lithium disilicate (LiO2 · 2SiO2 or LS2) samples with nucleation site saturation. The values of E and K0 calculated using the new kinetic equation agree well with those obtained by the Kissinger equation for the prenucleated a-Se, PS/PCS, and LS2 samples. The values of n indicate that volume crystallization is dominant in the bulk a-Se and LS2 samples, whereas surface crystallization is dominant in the powdered PS/PCS sample. These results for a-Se were confirmed by scanning and transmission electronic microscopy.


2005 ◽  
Vol 285 (1) ◽  
pp. 288-295 ◽  
Author(s):  
Antonio R. Cestari ◽  
Eunice F.S. Vieira ◽  
Joana D.S. Matos ◽  
Débora S.C. dos Anjos

Author(s):  
Е.В. Школьников

В статье [Школьников, 2019] исследовано влияние добавок олова на кинетические параметры ступенчатых превращений при изотермической объемной кристаллизации стекол AsSe1.5Snx (x = 0,13 и 0,20). Влияние концентрации свинца на характер и кинетические параметры реконструктивной кристаллизации стекол AsSe1.5Pbx изучено недостаточно. Методами измерения плотности, микротвердости, температурной зависимости электропроводности, рентгенофазового анализа и оптической микроскопии закаленных образцов исследованы кинетика и механизм превращений при объемной изотермической кристаллизации полупроводниковых стекол AsSe1.5Рвx (х = 0,025, 0,13) в интервале температур 210−340 °С. Анализ кинетики валовой кристаллизации стекол выполнен по данным измерения плотности с использованием уравнения Колмогорова-Аврами, обобщенного на ступенчатые и неполные изотермические превращения. Добавка 1 ат.% Pb к стеклу As2Se3 уменьшает примерно в 2 раза индукционный период выделения фазы As2Se3 и в 6-8 раз кинетический период полупревращения. Установлено, что на первой ступени изотермической ситаллизации стекол в низкотемпературном интервале 210−255 °С преобладает гомогенное зарождение и трехмерный рост нанокристаллов низкоомной фазы PbSe, инициирующей на второй ступени гетерогенное зарождение и двумерный рост кристаллов матричной высокоомной фазы As2Se3. Реконструктивная ступенчатая кристаллизация стекол AsSe1.5Pbx связана с непрерывным изменением химического состава остаточной стеклофазы и характеризуется интервалом уменьшающихся значений эффективной энергии активации. При длительной высокотемпературной термообработке стекол As2Se3 с 5 ат.% Pb в интервале 280–340 °С наблюдаются одновременно объемно-поверхностное расстекловывание фаз PbSe и As2Se3 и вторичные диффузионные процессы с понижением дисперсности, плотности, микротвердости и химической стойкости стеклокристаллов, а также с изменением носителей заряда с р-типа на n-тип. In the article [Shkolnikov, 2019] the effect of tin additives on the kinetic parameters of stepwise transformations during isothermal crystallization of AsSe1.5Snx glasses (x = 0.13 and 0.20) was investigated. The effect of lead concentration on the nature and kinetic parameters of reconstructive crystallization of AsSe1.5Pbx glasses was not studied enough. The kinetics and mechanism of transformations in volume isothermal crystallization of AsSe1.5Pbx semiconductor glasses (x = 0.025, 0.13) in the temperature range 210–340 °С were studied by measuring the density, microhardness, temperature dependence of electrical conductivity, X-ray phase analysis and optical microscopy. The analysis of the gross crystallization kinetics of glasses was performed according to the density measurement data using the Kolmogorov-Avrami equation, generalized to stepwise and incomplete isothermal transformations. The addition of 1 at.% Pb to the As2Se3 glass reduces the induction period of separation of the As2Se3 phase by about 2 times and the kinetic half-transformation period by 6-8 times. It was found that the first stage of isothermal glass sitallization in the low−temperature range 210-255 °C is dominated by homogeneous nucleation and three-dimensional growth of nanocrystals of low-resistance phase PbSe, initiating the second stage of heterogeneous nucleation and two-dimensional crystal growth of the matrix highresistance phase As2Se3.. The reconstructive stepwise crystallization of AsSe1.5Pbx glasses is associated with a continuous change in the chemical composition of the residual glass phase and is characterized by a range of decreasing values of the effective activation energy. During long-term high-temperature heat treatment of As2Se3 glasses with 5 at.% Pb in the range of 280–340 °C observed simultaneously volume-surface devitrification of the phases PbSe and As2Se3 and secondary diffusion processes with a decrease in dispersion, density, microhardness and chemical resistance of glass- crystals, as well as with the change of charge carriers from p-type to n-type


1970 ◽  
Vol 65 (1_Suppl) ◽  
pp. S104-S121 ◽  
Author(s):  
E. E. Baulieu ◽  
J. P. Raynaud ◽  
E. Milgrom

ABSTRACT A brief review of the characteristics of steroid binding proteins found in the plasma and in some target organs is presented, followed by some general remarks on binding »specificity« and binding parameters. Useful techniques for measuring binding parameters at equilibrium are reported, both those which keep the equilibrium intact and those which implicate its disruption. A concept is developed according to which the determination of a specific steroid binding protein is based on the »differential dissociation« of the several steroid binding complexes present in most biological mixtures. Methods which allow determination of the kinetic parameters of the binding systems are also presented. Various representations of the binding and therefore different modes of graphic representation and calculation are discussed, including the recent »proportion graph« method.


1974 ◽  
Vol 76 (1) ◽  
pp. 178-188 ◽  
Author(s):  
H. Lübbert ◽  
K. Pollow ◽  
R. Wagner ◽  
J. Hammerstein

ABSTRACT The effects of ethanol on kinetic parameters of placental Δ5-3β-hydroxysteroid dehydrogenase were studied. In the presence of high pregnenolone concentrations (50 μm, [S] > Km) the microsomal enzyme preparation exhibited an almost linear increase in activity as the ethanol concentration in the medium was raised from 2.5 to 15 % (v/v). At lower substrate concentrations ([S] << Km) ethanol caused inhibition. Other effects of ethanol were: linearity of product formation with time was prolonged; the maximal velocity was markedly increased; the Km for pregnenolone slightly decreased with increasing ethanol concentrations (2.5 to 10 %, v/v) whereas the Km for NAD remained the same. The pH and temperature optima of the reaction were unaffected by ethanol. Other organic solvents caused similar effects.


2019 ◽  
Vol 3 (2) ◽  
pp. 27
Author(s):  
Emma Savitri ◽  
Natalia Suseno ◽  
Tokok Adiarto

Many mass-transfer applications have used chitosan membrane in separation processes. This research applied crosslinked chitosan membrane to sterillize bacterial growth media. Chitosan membranes having 79 % DD were produced by casting and drying chitosan solution. The images of the membrane were characterized by SEM and other characterizations such as permeability, permselectivity and tensile strength were investigated. The flux increased with longer submersion period but the rejection decreased. Otherwise, the flux decreased and rejection increased in line with an increase in curing temperature. Tensile strength increased with the increase of submersion period and curing temperature. The optimum conditions of crosslinking process are 2 hours of submersion periods and curing temperature at 90 oC.  It gives flux 5.8930 L/jam.m2, rejection 97.47 % and tensile strength 49640 kN/m2


2017 ◽  
Vol 68 (5) ◽  
pp. 903-907
Author(s):  
Ecaterina Anca Serban ◽  
Ioana Diaconu ◽  
Elena Ruse ◽  
Georgiana Ileana Badea ◽  
Adriana Cuciureanu ◽  
...  

Indole-3-acetic acid is a growth phytohormone considered the most important representative of auxin class. This paper presents the assessment of some kinetic parameters in the process of transport of indole-3-acetic acid taking into consideration the kinetic model of consecutive irreversible first order reactions. It was pursued the influence upon the process of parameters such as: feed phase concentration, stripping phase concentration in the presence of two type carriers: tributyl phosphate (TBP) and trioctylphosphine oxide (TOPO). Depending on these transport parameters were calculated kinetics parameters such as: pseudo-first-order apparent membrane entrance and exit rate constants, the maximum flux at the entrance and exit out of the membrane. The highest values of the transport flux is obtained in the presence of carrier trioctylphosphine oxide (TOPO) at the concentration in the feed phase of 10-4 mol/L indole-3-acetic acid and a concentration of 10--2mol/L NaOH in the stripping phase.


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